Britain’s Johanna Konta pulled off the biggest win of her career as she knocked out ninth seed Garbine Muguruza to reach the third round of the US Open.

Muguruza has made the French Open quarter-finals and the final at Wimbledon this year, but could not find an answer to Konta, who sealed a shock 7-6 (7/4) 6-7 (4/7) 6-2 victory.

Konta had only managed one grand slam win prior to this tournament, but she now has two in three days and goes through to face Germany’s Andrea Petkovic in round three.

The British No 2 now has 15 consecutive victories since losing to Maria Sharapova at Wimbledon, but this was the first against an opponent in the top 80 and certainly her most impressive.

It came in three hours and 23 minutes, which set a new US Open record for a women’s match since the tie-break was introduced in 1970.

Muguruza arrived in Flushing Meadows on the back of first-round defeats in both Toronto and Cincinnati, and she looked out of sorts throughout, producing 13 double faults and 59 unforced errors.

This should not detract from the display of Konta, however, who appears to be a player transformed under Spanish coach Esteban Carril and now has a realistic chance of making the last 16.

“I’m just so tired,” Konta said.

“She probably didn’t play her best, but she’s an incredible fighter and no matter what level she brings to the court she always brings her top-10 mentality.

“I had to fight for every point and I’m just really happy to come back another day.”

Konta lost the opening six points in a row but soon found her rhythm, opening up seven break points in two games, either side of a service hold to love.

It took a Muguruza double fault for Konta to finally convert, but the break was no less than she deserved as the Briton moved 5-3 ahead.

Konta spurned two set points and then handed the break back as the Spaniard forced a tie-break. Undeterred, Konta pressed ahead again and sealed the set when another loose Muguruza forehand drifted long.

Muguruza broke Konta at the crucial time in the second set to lead 5-4. The Spaniard’s serving problems continued to fester, however, and another double fault allowed Konta back in.

Muguruza closed out the set in a tie-break and Konta took a toilet break, presumably to recover her focus.

She returned rejuvenated, breaking Muguruza’s serve once and then again to storm 4-0 clear and while the Spaniard stemmed the tide, it was only temporary, as a forehand long confirmed Konta’s momentous win.